This invention is related to a contact lens with visible marking indicia. More particularly, this invention is related to a contact lens with visible marking indicia created by a laser etching system, and methods for making the marks.
A variety of methods are known for placing marking indicia on contact lenses. These techniques generally involve either applying a mark directly on the contact lens, or for cast molded contact lenses, placing an inversion mark on the mold insert or molded casting cup so that the mark gets reproduced onto the lens-during the cast-molding process. Typically, the marking indicia is used to identify the source of the lens, to identify a specific orientation in an asymmetric lens, or to identify the front or back surface of a lens.
One such method for making an inversion mark involves the use of an electric discharge to burn the mark into a metal mold insert. The electrodes are shaped to correspond to the mark and placed in proximity to the mold insert where an electric discharge melts the mark in the surface of the insert. The size and shape of the letters in the mark are limited by the minimum 0.10 mm radius possible with wire-cut electrodes. The electric discharge can be a fire hazard and the equipment must have built in extinguishers.
Another method for making marks is to use a diamond point engraver to cut the mark into the surface of the mold insert. Some difficulties with this technique is that the depth of penetration is not uniform because of the difficulty aligning the arc of the cutter with the curved surface of the insert. Also, the profile of the mark is limited by the shape of the cutter.
Other techniques for placing indicia on contact lens, either directly or indirectly through marking the mold insert, include printing a visible mark on the lens, dyeing a visible mark on the lens, placing sphero-cylindrical optical marking elements on the lens, chemically etching the mark on the mold insert, and laser-writing a mark in the mold insert. Still, there is room for improvement for new marking techniques in terms of visibility, economics, wearer comfort, ease of manufacture, and manufacturing safety.
This invention is directed to an inversion mark on a cast molded contact lens, and a process for making that inversion mark. In one aspect of this invention, there is provided a contact lens having visible marking indicia on the lens. The marking indicia includes a plurality of recessed spots having side walls. The area of maximum depth of the recessed spots is generally proximate to the side walls around the perimeter of the spot. The recessed spots also include a substantially convex bottom surface. The convex bottom surface has a central surface area at a shallower depth than the maximum depth of the recessed spot.
In another aspect of the invention, there is provided a method of making a cast molded inversion mark in contact lenses. This method includes forming a plurality of recessed spots in a predetermined pattern in a metal mold insert. Preferably, the recessed spots have a substantially convex bottom surface. The method proceeds by injection molding thermoplastic casting cups with the mold inserts, and then casting a contact lens with the casting cups. By this process the recessed spots in the predetermined pattern in the mold insert are reproduced as raised spots on the casting cup, which are then reproduced as visible recessed spots in the predetermined pattern on the contact lens.
This invention further provides, in a third aspect, a method of making a cast molded inversion mark in a contact lens mold insert. The method includes the acts of providing a metal mold insert used for making contact lens casting cups, disposing over the insert a laser mask that has an array of holes. Then the method proceeds by projecting one or more laser beam pulses through the mask to etch recessed spots in the surface of the insert. The method further includes scanning the insert and mask synchronously with respect to the laser beam pulses thereby forming the inversion mark on the mold insert.
This invention has the advantage of providing a highly visible mark on a wet hydrogel contact lens that is visible when the lens is handled, and when worn on the eye, the mark may be seen easily by an eye-care professional. Moreover, no additional materials, such as inks or dyes, need to be added to the lens to enhance the visibility of the marks.